Today: Climate change, marine life in the acidic ocean

Nov 21, 2022 

By Philip Pearson

Scientists at the Natural History Museum have now re-examined a clutch of Challenger’s specimens collected 150 years ago at Station 272, located in the mid-Pacific Ocean. The specimens they reviewed are foraminifera, minute, millimeter-sized single cell organisms with a thin shell usually made from calcium carbonate, such as these.

Source: British geological Survey

Ocean acidification is caused by the rapidly increasing concentration of carbon (CO2) in the atmosphere due to human activity. As CO2 levels continue to rise, more of the gas dissolves into the world’s oceans. The waters become more acidic, and some of the smallest yet most important organisms in our ocean’s food chain are beginning to struggle.

During the expedition, Challenger scientists routinely stored and labelled their specimens in sample jars such as the one shown here. The sample jars are kept at the Natural History Museum, London.

Comparing the Challenger’s findings of specimens that were alive at the time they were retrieved (8 September in 1875) with modern samples taken from the same part of the Pacific Ocean by the Tara Expeditions  (2009–2016), a team of the museum’s scientists found that:

  • single-celled organisms (known as planktonic foraminifera) are now failing to build shells of the same thickness, due to increasing ocean acidity.
  • all modern specimens had up to 76% thinner shells than their historic counterparts, which corresponds to a period of profound change in our oceans.

Challenger specimen: Neogloboquadrina acostaensis.

According to Dr Lyndsey Fox, who led the scientific team, ‘There have been dramatic reductions in shell thickness in some species of foraminifera, though less so in others.’ This Challenger specimen is Neogloboquadrina acostaensis. In this Nano-CT scan, warm colours indicate areas of relatively thicker shell.


Tara Expeditions vessel

Re-examining the Challenger specimens and the scientists’ own Sounding notebooks provide the first direct evidence of how ocean acidification is impacting carbonate (shell) producing marine life over a long time period in modern oceans.

Challenger Sounding books, Natural History Museum: #ChallengerRevisited

A Challenger sample jar. It contains specimens from Sample Station 302, located on the ‘East Coast of S. America,’ dated 28 December 1875. Natural History Museum


Nature, January 2020, Quantifying the Effects of Climate Change on Plankton